This invention relates generally to a device for measuring the relative position and the speed of a rotating moving shaft, which device consists of an annular magnetic encoder, with multipolar magnetization, which is integrally connected to and concentric with the shaft, and of a sensor having at least two separate sensing elements, with Hall effect or with magnetoresistance devices, connected to a fixed frame. The invention relates more particularly to novel designs of multipolar encoders which make it possible to simplify the final assembly of the measuring devices and to use a sensor of a unique type.
It is known how to measure the speed and the position of a moving part by means of a sensor with two sensing elements arranged opposite a multipolar magnetic encoder. Generally, the geometric position of the two sensing elements is adjusted so that their centers are in quadrature in the alternating or sinusoidal magnetic field of the magnet. This situation is achieved when the distance between the centers of the sensing element corresponds to an odd number of quarters of the magnetic period of the encoder. The electrical signals delivered by the sensing elements are then in quadrature.
When, in a device which is not geometrically controlled, the signals delivered by the sensing elements are sinusoidal in form, it is also known how to control them in quadrature by appropriate electronic signal processing.
In the case of a rotation measurement, an arrangement consists of mounting an encoder concentrically on and integrally connected to a rotating shaft, which encoder is in the form of an annular disk, magnetized on one of its faces. The magnetic transitions defined between the sectors with north polarity and the sectors with south polarity are generally marked by spokes of the disk or of the encoder ring. The multipolar magnet consequently consists of a number equal to 2 m circular sectors or poles with angle .pi./m, with alternately opposite polarities, which determine m sectorial periods of 2.pi./m angular value.
The geometric control in quadrature in the magnetic field of the sensing elements of the sensor requires that the following dimensional equation be satisfied: EQU d=2R * sin [(2n+1) * .pi./4m]
where: d is the distance separating the centers of the sensing elements of the sensor,
R is the reading radius of the encoder where the sensing elements are placed, and PA1 N is a whole number, which can be negative, zero or positive, and which allows the establishment of the states of quadrature.
This equality expresses that, for a given state of quadrature, for example, one-fourth, three-fourths or five-fourths of a period, and for a chosen number of periods m of the magnetic encoder, there exists an unambiguous relation between the distance d and the reading radius R.
One problem resulting from this arrangement is that for each new concept of a measuring device modifying either the number of periods of the encoder or the position of the sensor on the reading radius R, it is necessary to create a new sensor with two appropriately spaced sensing elements to ensure the state of quadrature, which increases the manufacturing costs. The manufacturing technologies used are preferably those which use step-and-repeat methods of sensing elements in discrete components on a support, where the precision of positioning is insufficient to allow the elimination of the need for control at the end of the assembly of each measuring device constructed.
Another problem resulting from this arrangement is due to the fact that the function of the frame which is used as a support for the sensor is generally ensured by parts with low precision of execution, which results in a lack of precision in the positioning of the sensor on the reading radius of the encoder and thus a lack of precision in the state of quadrature of the signals, if each measuring device is not controlled in the final assembly.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.